This invention relates generally to vacuum electron devices. More particularly, the invention relates to vacuum electron devices that comprise a photonic bandgap (PBG) structure.
Vacuum electron devices or microwave tubes are important sources of high power microwave radiation for use in industrial heating, plasma heating, radar, communications, accelerators, spectroscopy and many other applications. Extension of the operating frequency of these sources to higher frequency is of great interest and would open up many new applications. Obstacles exist to the extension of the operating frequency.
First, as the frequency increases to the millimeter wave range, cavities operating in the fundamental mode of a waveguide (rectangular or circular, for example) require dimensions of less than the wavelength so that accurate fabrication is difficult and expensive. Dimensions of less than a millimeter are not uncommon. Second, the heat load per unit area on resonator walls becomes excessive at high power in such resonators. Third, it can become difficult to pass electron beams through small structures without beam interception.
The use of overmoded cavities has been attempted to alleviate the problems of excessive heating and difficulty of fabrication. However, the small spacing between modes in conventional overmoded cavities leads to mode competition. Mode competition is a limiting factor in the design and operation of gyrotron amplifiers and oscillators operating in the millimeter wave band. It is also a serious obstacle to building conventional slow wave devices such as traveling wave tubes and klystrons with overmoded structures in the microwave and millimeter wave band. Indeed, the beam tunnel in a high-power periodic permanent magnet (PPM) focusing klystron amplifier is typically designed to provide cutoff at the second harmonic in order to prevent self-oscillation.
The vacuum electron device with a PBG structure can include a PBG structure that is capable of overmoded operation, as well single mode operation. PBG structures are, in some embodiments, two-dimensional (2D) or three-dimensional (3D) periodic structures with restricted transmission bands at certain frequencies. Such vacuum electron devices include gyrotron oscillators and amplifiers, traveling wave tubes, traveling wave tube amplifiers, klystrons, microwave tubes, and the like. The device with the PBG structure can include a single cavity, or the device can include a plurality of cavities. The PBG structure permits the device to operate more efficiently.
PBG cavities offer several advantages, including, but not limited to, an oversized structure that offers ease of fabrication; a structure that is suitable for high frequency operation; and a structure that can include an absorbing peripheral boundary. PBG structures can be used to provide higher order mode discrimination. Coupling into a PBG cavity can be performed using a variety of coupling schemes, and the coupling can be optimized. Coupling into a PBG cavity in some embodiments involves distributed coupling. Distributed coupling results in relatively small disturbance of the resonant mode frequency when compared with conventional hole coupling.
In one aspect, the invention relates to a tunable photonic bandgap structure, comprising a photonic bandgap structure having a plurality of members, at least one member of which is movable. In one embodiment, at least one of the plurality of movable members comprises a rectilinear structure.
In another aspect, the invention features a temperature-controlled photonic bandgap structure, comprising a photonic bandgap structure having a plurality of members, at least one member of which is temperature controlled. In one embodiment, at least one temperature-controlled member comprises a surface that is temperature controlled by contact with a fluid.
In another aspect, the invention concerns a tunable, temperature controlled photonic bandgap structure, comprising a photonic bandgap structure having a plurality of members, wherein at least one member is movable, and wherein at least one member is temperature controlled. In one embodiment, the photonic bandgap structure comprises the plurality of members disposed in a multi-dimensional array. In one embodiment, the multi-dimensional array is a periodic array.
In yet another aspect, the invention relates to an apparatus for providing mode-selected microwave radiation. The apparatus comprises a vacuum electron device microwave generator creating microwave radiation having a plurality of modes, and a temperature controlled photonic bandgap structure in communication with the vacuum electron device microwave generator. The PBG receives the microwave radiation and selects one of the plurality of modes of the microwave radiation to be propagated. The photonic bandgap structure comprises a plurality of members disposed in a two-dimensional array wherein at least one member is temperature controlled.
In a still further embodiment, the invention features an apparatus for providing mode-selected microwave radiation. The apparatus comprises a vacuum electron device microwave generator creating microwave radiation having a plurality of modes, and a tunable photonic bandgap structure in communication with the vacuum electron device microwave generator. The PBG receives the microwave radiation and selects one of the plurality of modes of the microwave radiation to be propagated. The photonic bandgap structure comprises a plurality of members disposed in a two-dimensional array wherein at least one member is movable.
In a further aspect, the invention relates to an apparatus for providing mode-selected microwave radiation. The apparatus comprises a vacuum electron device microwave generator creating microwave radiation having a plurality of modes, and a tunable photonic bandgap structure in communication with the vacuum electron device microwave generator to receive the microwave radiation and to select one of the plurality of modes of the microwave radiation to be propagated, the photonic bandgap structure comprising a plurality of members disposed in a two-dimensional array wherein at least one member is movable, and wherein at least one member is temperature controlled.
In yet another aspect, the invention features an apparatus for providing mode-selected microwave radiation. The apparatus comprises a microwave generator means for creating microwave radiation having a plurality of modes, and a temperature controlled photonic bandgap means for receiving the microwave radiation and for selecting one of the plurality of modes of the microwave radiation to be propagated, the temperature controlled photonic bandgap means in communication with the microwave generator means.
In a still further aspect, the invention is involved with an apparatus for providing mode-selected microwave radiation. The apparatus comprises a microwave generator means for creating microwave radiation having a plurality of modes, and a tunable photonic bandgap means for receiving the microwave radiation and for selecting one of the plurality of modes of the microwave radiation to be propagated, the tunable photonic bandgap means in communication with the microwave generator means.
In one aspect, the invention features the devices themselves including the PBG structure. In another aspect, the invention relates to the methods of use of the devices with the PBG structure. In a further aspect, the invention features methods of manufacturing the devices with the PBG structure. In yet a further aspect, the invention relates to methods of simulating the PBG structure and simulating the behavior of the PBG structure.
In some embodiments, the PBG structure enables the device to handle higher powers and to have a larger size than a similar device without a PBG structure. In some embodiments, the PBG structure provides features such as filtering, amplification, and mode selection. In some embodiments, the PBG structure is an all-metal structure. In an alternative embodiment, the PBG structure is a structure that comprises both metals and dielectric materials. The PBG structure can have a plurality of members, such as cylindrical metal rods disposed axially therein. The members are movable, and can extend along the axial direction for a fixed distance, or can extend along the axial direction for a distance that can be varied. The members can be disposed in an array on a plane perpendicular to the axial direction. One or more of the members can be removed from the array to introduce a defect into the PBG structure. In some embodiments, the PBG structure enables a relaxation of the structural and mechanical precision otherwise needed in fabricating operational devices. In one embodiment, the members, for example, metal rods, can be temperature controlled by flowing a fluid, such as water, therethrough.
In some aspects, the invention relates to a method of modeling a PBG structure. The method includes the use of a finite element computer code for calculating eigenmodes in periodic metallic structures, including 2D and 3D structures. The modeling method includes calculations for the determination of the bulk properties of wave propagation in PBG structures, and calculations of the eigenmodes that appear in PBG cavities.
The foregoing and other objects, aspects, features, and advantages of the invention will become more apparent from the following description and from the claims.